Merriam-Webster Collegiate Dictionary - ratchet

 I. noun  also rachet  Etymology: alteration of earlier rochet, from French, alteration of Middle French rocquet ~, bobbin, of Germanic origin; akin to Old High German rocko distaff — more at rock  Date: 1654  1. a mechanism that consists of a bar or wheel having inclined teeth into which a pawl drops so that motion can be imparted to the wheel or bar, governed, or prevented and that is used in a hand tool (as a wrench or screwdriver) to allow effective motion in one direction only  2. a pawl or detent for holding or propelling a toothed wheel  II. verb  also rachet  Date: 1972  transitive verb to cause to move by steps or degrees — usually used with up or down tried to ~ down the debt  intransitive verb to proceed by steps or degrees